1. Field of the Invention
The present invention relates to a high-temperature motor pump and a method of operating thereof, and more particularly to a high-temperature motor pump for pumping a high temperature liquid for use in a boiler system or a nuclear power plant and a method of operating thereof.
2. Description of the Related Art
A conventional high-temperature motor pump comprises a pump portion for pumping a high temperature liquid and a motor portion having a motor for driving the pump portion. These portions are housed in a liquid-tight chamber, and a coolant flow is provided in the motor portion for cooling the motor to pass through a narrow gap between a stator and a rotor.
One example of such a pump is disclosed in Japanese Laid-Open Patent Application No. 1-174231, in which a coolant is cooled by an external heat exchanger and introduced into the motor.
However, in the above motor pump, since the coolant flows through the narrow gap between a stator and a rotor in the motor to conduct cooling, if the coolant temperature is excessively low, a high viscosity of the coolant leads to a high friction loss.